[clang] Clang crashes when an objective C exception is attempted to be caught when `-fwasm-exceptions` is enabled on a wasm{32,64} target

[Frityet]

Crash info

Reproducer:

extern void f();

int main()
{
	@try {
		f();
	} @catch(id) {

	}
}

Command:

# Crash reproducer for Homebrew clang version 19.1.6
# Driver args: "t.m" "-target" "wasm32-unknown-none" "-fwasm-exceptions"
# Original command:  "/usr/local/Cellar/llvm/19.1.6/bin/clang-19" "-cc1" "-triple" "wasm32-unknown-none" "-emit-obj" "-dumpdir" "a-" "-disable-free" "-clear-ast-before-backend" "-disable-llvm-verifier" "-discard-value-names" "-main-file-name" "t.m" "-mrelocation-model" "static" "-mframe-pointer=none" "-ffp-contract=on" "-fno-rounding-math" "-mconstructor-aliases" "-target-feature" "+exception-handling" "-mllvm" "-wasm-enable-eh" "-target-feature" "+multivalue" "-target-feature" "+reference-types" "-target-cpu" "generic" "-fvisibility=hidden" "-debugger-tuning=gdb" "-fdebug-compilation-dir=/Users/frityet/Documents/scratch" "-target-linker-version" "1022.1" "-fcoverage-compilation-dir=/Users/frityet/Documents/scratch" "-resource-dir" "/usr/local/Cellar/llvm/19.1.6/lib/clang/19" "-internal-isystem" "/usr/local/Cellar/llvm/19.1.6/lib/clang/19/include" "-internal-isystem" "/include" "-ferror-limit" "19" "-fgnuc-version=4.2.1" "-fskip-odr-check-in-gmf" "-fobjc-runtime=gnustep" "-fobjc-encode-cxx-class-template-spec" "-fobjc-exceptions" "-fexceptions" "-exception-model=wasm" "-fcolor-diagnostics" "-o" "/var/folders/ps/cqv_3ytx5nn59k5q3k17th500000gn/T/t-e67633.o" "-x" "objective-c" "t.m"
 "/usr/local/Cellar/llvm/19.1.6/bin/clang-19" "-cc1" "-triple" "wasm32-unknown-none" "-emit-obj" "-dumpdir" "a-" "-disable-free" "-clear-ast-before-backend" "-disable-llvm-verifier" "-discard-value-names" "-main-file-name" "t.m" "-mrelocation-model" "static" "-mframe-pointer=none" "-ffp-contract=on" "-fno-rounding-math" "-mconstructor-aliases" "-target-feature" "+exception-handling" "-mllvm" "-wasm-enable-eh" "-target-feature" "+multivalue" "-target-feature" "+reference-types" "-target-cpu" "generic" "-fvisibility=hidden" "-debugger-tuning=gdb" "-fdebug-compilation-dir=/Users/frityet/Documents/scratch" "-target-linker-version" "1022.1" "-fcoverage-compilation-dir=/Users/frityet/Documents/scratch" "-ferror-limit" "19" "-fgnuc-version=4.2.1" "-fskip-odr-check-in-gmf" "-fobjc-runtime=gnustep" "-fobjc-encode-cxx-class-template-spec" "-fobjc-exceptions" "-fexceptions" "-exception-model=wasm" "-fcolor-diagnostics" "-x" "objective-c" "t-3e83b8.m"

Cannot be reproduced on godbolt due to the fact that godbolt objective C does not allow for clang to be selected as the compiler for some reason?

[Frityet]

the code inside the @try can be replaced with anything that could throw an exception, so doing @throw (id)0 also works

[Frityet]

I have been investigating a fix but my PC keeps crashing when I try and compile LLVM :(, still working on a fix (for this issue, and my PC too)

[pinskia]

Cannot be reproduced on godbolt due to the fact that godbolt objective C does not allow for clang to be selected as the compiler for some reason?

Yes you can, you just need to use the -x option. That is -xobjective-c -target wasm32-unknown-none -fwasm-exceptions can reproduce this with the x86_64 clang. See https://godbolt.org/z/nMqjGhG1z .

[Frityet]

Cannot be reproduced on godbolt due to the fact that godbolt objective C does not allow for clang to be selected as the compiler for some reason?

Yes you can, you just need to use the -x option. That is -xobjective-c -target wasm32-unknown-none -fwasm-exceptions can reproduce this with the x86_64 clang. See https://godbolt.org/z/nMqjGhG1z .

Nice! Thank you!

[aheejin]

Sorry for the late reply. Running the command line you gave produces landingpad instructions used for Itanium EH, not catchpads and cleanuppads currently by Wasm EH. But I also noticed what command line you gave was not the clang one but clang-19. How did you run in clang to compile your code in the first place?

To be clear, I don't think Wasm EH has been tested with Objective C code so far, and we likely need some more code in Clang to make it work.

[Frityet]

Sorry for the late reply. Running the command line you gave produces landingpad instructions used for Itanium EH, not catchpads and cleanuppads currently by Wasm EH. But I also noticed what command line you gave was not the clang one but clang-19. How did you run in clang to compile your code in the first place?

The command I used to compile originally was just

clang -target wasm32-unknown-none -fwasm-exceptions test.m

To be clear, I don't think Wasm EH has been tested with Objective C code so far, and we likely need some more code in Clang to make it work.

Any ideas of what needs to be done? I ain't too sure with clang's codebase

[llvmbot]

@llvm/issue-subscribers-backend-webassembly

Author: None (Frityet)

[Crash info](https://gist.github.com/Frityet/83fa2c7eee836515f871d59c594e9479)

Reproducer:

extern void f();

int main()
{
	@<!-- -->try {
		f();
	} @<!-- -->catch(id) {

	}
}

Command:

# Crash reproducer for Homebrew clang version 19.1.6
# Driver args: "t.m" "-target" "wasm32-unknown-none" "-fwasm-exceptions"
# Original command:  "/usr/local/Cellar/llvm/19.1.6/bin/clang-19" "-cc1" "-triple" "wasm32-unknown-none" "-emit-obj" "-dumpdir" "a-" "-disable-free" "-clear-ast-before-backend" "-disable-llvm-verifier" "-discard-value-names" "-main-file-name" "t.m" "-mrelocation-model" "static" "-mframe-pointer=none" "-ffp-contract=on" "-fno-rounding-math" "-mconstructor-aliases" "-target-feature" "+exception-handling" "-mllvm" "-wasm-enable-eh" "-target-feature" "+multivalue" "-target-feature" "+reference-types" "-target-cpu" "generic" "-fvisibility=hidden" "-debugger-tuning=gdb" "-fdebug-compilation-dir=/Users/frityet/Documents/scratch" "-target-linker-version" "1022.1" "-fcoverage-compilation-dir=/Users/frityet/Documents/scratch" "-resource-dir" "/usr/local/Cellar/llvm/19.1.6/lib/clang/19" "-internal-isystem" "/usr/local/Cellar/llvm/19.1.6/lib/clang/19/include" "-internal-isystem" "/include" "-ferror-limit" "19" "-fgnuc-version=4.2.1" "-fskip-odr-check-in-gmf" "-fobjc-runtime=gnustep" "-fobjc-encode-cxx-class-template-spec" "-fobjc-exceptions" "-fexceptions" "-exception-model=wasm" "-fcolor-diagnostics" "-o" "/var/folders/ps/cqv_3ytx5nn59k5q3k17th500000gn/T/t-e67633.o" "-x" "objective-c" "t.m"
 "/usr/local/Cellar/llvm/19.1.6/bin/clang-19" "-cc1" "-triple" "wasm32-unknown-none" "-emit-obj" "-dumpdir" "a-" "-disable-free" "-clear-ast-before-backend" "-disable-llvm-verifier" "-discard-value-names" "-main-file-name" "t.m" "-mrelocation-model" "static" "-mframe-pointer=none" "-ffp-contract=on" "-fno-rounding-math" "-mconstructor-aliases" "-target-feature" "+exception-handling" "-mllvm" "-wasm-enable-eh" "-target-feature" "+multivalue" "-target-feature" "+reference-types" "-target-cpu" "generic" "-fvisibility=hidden" "-debugger-tuning=gdb" "-fdebug-compilation-dir=/Users/frityet/Documents/scratch" "-target-linker-version" "1022.1" "-fcoverage-compilation-dir=/Users/frityet/Documents/scratch" "-ferror-limit" "19" "-fgnuc-version=4.2.1" "-fskip-odr-check-in-gmf" "-fobjc-runtime=gnustep" "-fobjc-encode-cxx-class-template-spec" "-fobjc-exceptions" "-fexceptions" "-exception-model=wasm" "-fcolor-diagnostics" "-x" "objective-c" "t-3e83b8.m"

Cannot be reproduced on godbolt due to the fact that godbolt objective C does not allow for clang to be selected as the compiler for some reason?